Heat sink with fins

ABSTRACT

A heat sink with fins comprising a group of heat dissipating fins which comprise combination of heat dissipating fins made of at least two kinds of metals having different heat conductivity, and a metal base plate on which surface portion the group of heat dissipating fins are densely jointed.

RELATED APPLICATIONS

This application is a continuation-in-part, and hereby incorporates byreference the entire disclosure, of co-pending U.S. patent applicationSer. No. 10/055,619, entitled “HEAT SINK WITH FINS”, which was filed onJan. 22, 2002, now U.S. Pat. No. 6,554,060.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat sink with fins used for coolingelectronic devices, and in particular relates to the heat sink with finsin which heat dissipating fins are jointed on a metal base plate.

2. Description of the Related Art

In order to dissipate the heat generated by a semiconductor chip, whichis increasing year by year, there is known a method in which a heat sinkis attached in close contact to the semiconductor chip so as to transferthe heat from the semiconductor chip to the heat sink, and dissipatesame. A conventional heat sink has a metal flat base plate so as for thesemiconductor chip to be closely contacted thereon, and has constructionthat plural heat dissipating fins of metal thin plates are jointed onthe surface opposite to the surface of the base plate on which thesemiconductor chip is attached.

In the heat sink with fins having the above-mentioned construction, theheat generated by the semiconductor chip transfers from thesemiconductor chip to the metal base plate which is closely contactedthereto, and spreads over the base plate, and thus spread heat isdissipated into air or the designated place by the metal heatdissipating fins which are fixed on the surface of the metal base plate.In addition, there is provided a one-piece heat sink made of forgedaluminum as one of the conventional heat sinks. However, there is aproblem in which the one-piece heat sink made of forged aluminum do notattain enough heat dissipating effect, because required number of heatdissipating fins are not formed due to the technical difficulty byforging to shorten the pitch between the heat dissipating fins for therequired level of fin-density.

In order to solve the above-mentioned problem and obtain much moreexcellent heat dissipating effect, there is proposed a method instead ofa one-piece heat sink, in which a base plate and heat dissipating finsare separately manufactured and the heat dissipating fins are jointed ona surface of the base plate by means of brazing or mechanical joint.

The mechanical joint in which the heat dissipating fins are jointedmechanically on a surface portion of the base plate is superior to thebrazing, because manufacturing cost of brazing is higher than that ofmechanical joint.

As shown in FIG. 4, when the size of the semiconductor chip 30 and thebase plate 22 are compared, the semiconductor chip 30 is much smallerthan the base plate 22. Therefore it is necessary to spread the heatgenerated by the small semiconductor chip 30 all over the large baseplate 22 by using the base plate made of materials having high heatconductivity such as copper, aluminum or the like. In particular, sincethe copper is excellent in heat conductivity, the copper is known as amaterial for the base plate of the heat sink with fins. However, sincethe copper is heavy and the copper base plate must be in direct contactwith the semiconductor chip, there is required some reinforcingconstruction (for example: applying a jointing device for protecting acircuit board or the like) to reduce the damage that the weight of thecopper base plate imposes onto the semiconductor chip.

Furthermore, electronic devices become remarkably lighter and smaller,which makes it difficult to use the copper base plate because the chanceto use such heavy copper base plate is reducing and it becomes difficultto secure the space for installing the copper base plate. On the otherhand, when the semiconductor chip becomes more integrated and theprocessing capacity becomes higher, the heat generated by thesemiconductor chip becomes larger. Therefore, further higher heatdissipating effect is required for stable operation of the semiconductorchip or the like.

As described above, it becomes difficult to use the copper base platedue to the heavy weight thereof in spite of the excellent heatconductivity. Therefore, when aluminum is to be used for material of thebased plate, it is necessary to satisfy the requirement of furtherincreasing heat dissipating effect of the heat sink.

In the heat sink having construction that the heat dissipating fins aremechanically fixed on a surface of the base plate, the base plate hasthe following temperature distribution when the heat dissipation is inthe stable condition. More specifically, the temperature is the highestin the central portion of the base plate to which the semiconductor chipis attached in close contact and, the temperature becomes lower as theportion in the base plate moves farther from the semiconductor chip.

In addition, the heat dissipating fins which are fixed and thermallyconnected to a surface of the base plate has the following temperaturedistribution. More specifically, the temperature is the highest in theheat dissipating fins locating in the central portion of the base plateto which the semiconductor chip is attached in close contact, and thetemperature is the lowest in the heat dissipating fins locating in theend portions of the base plate which are far apart from the centralportion.

Furthermore, the heat dissipating fin itself has the followingtemperature distribution along the height direction. More specifically,the temperature is the highest in the bottom portion of the fin which isfixed and thermally connected to the base plate and, the temperaturebecomes lower as the portion moves farther from the bottom portion.

It proves that the heat is transferred by heat conduction in the heatdissipating fin.

However, it is desirable to minimize difference of temperature acrossthe entire portion of the heat sink with fins, from the heat dissipatingefficiency point of view. As described above, lately, the heat generatedby the semiconductor chip is increasing, and at the same time, thesemiconductor chip is more downsized, which tends to rapidly increasethe heat density. Therefore it is urgently required to improve heatdissipating efficiency of the heat sink with fins (for example,increasing density of the heat dissipating fins fixed on the base plate,or using a heat pipe in the base plate, or the like). In particular, itis strongly demanded to increase heat dissipating efficiency by reducingdifference of temperature in the portions of the above-mentioned heatsink with fins.

As mentioned above, there is a problem in which a one-piece heat sinkmade of forged aluminum does not attain enough that dissipating effect,because the required number of the heat dissipating fins are not formeddue to the technical difficulty by forging to shorten the pitch betweenfins for the required level of fin-density. Furthermore, there is also aproblem in which using the heavy copper base plate becomes difficult dueto the heavy weight thereof even if the heat conductivity is excellent.Therefore, it is strongly demanded to increase heat dissipatingefficiency of the heat sink with fins having construction that the heatdissipating fins are mechanically fixed on a surface of the aluminumbase plate.

However the heat sink having construction that the heat dissipating finsare mechanically fixed on a surface of the aluminum base plate hasproblem in heat dissipating efficiency, because there are temperaturedifference both in the base plate and the heat dissipating fins.

SUMMARY OF THE INVENTION

There is provided according to the invention a heat sink with finscomprising groups of heat dissipating fins which comprise at least twogroups of heat dissipating fins, which are made of at least two kinds ofmetals having different heat conductivity, said heat dissipating fins ofeach group being made of same metal, respectively and a metal base plateon which surface portion said groups of heat dissipating fins aredensely jointed, wherein a part of said at least two groups of heatdissipating fins are integrally formed with said metal base plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of a heat sink with fins of the invention.

FIG. 2 shows another embodiment of a heat sink with fins of theinvention.

FIG. 3 is a graph to show relationship between copper fin ratio (ratioof number of heat dissipating fins made of copper in total number ofheat dissipating fins) and thermal resistance.

FIG. 4 shows a heat sink to which a semiconductor chip or the like isattached in close contact.

FIG. 5 shows another embodiment of a heat sink with fins of theinvention.

DETAILED DESCRIPTION OF THE PREFERABLE EMBODIMENTS

With reference to the attached drawings, the heat sink with fins of thepresent invention is explained in detail.

To solve the problem in the conventional art, the present inventors haveintensively studied. As a result, it has been found that difference oftemperature in the base plate can be reduced by the following: the heatdissipating fins are made of two kinds of metals having different heatconductivity, the heat dissipating fins made of the metal having higherheat conductivity are located on the portion of the base plate close toa heat generating element such as a semiconductor chip or the like, andthe heat dissipating fins made of the metal having relatively lower heatconductivity are located in the remaining portion of the base plate.

It has also been found that difference of temperature in the heatdissipating fins which are located on the portion of the base plateclose to the heat generating element can be reduced by using the metalhaving high heat conductivity.

More specifically, the heat dissipating efficiency of the heat sink canbe improved by reducing difference of temperature both in the base plateand in the heat dissipating fins by the following: using the aluminumfor the base plate, using copper for the heat dissipating fins locatingclose to the heat generating element such as a semiconductor chip or thelike, and using aluminum for the heat dissipating fins located in theremaining portion of the base plate.

One of the objects of the invention is to solve the problem in theconventional art and to provide a heat sink with fins having high heatdissipating efficiency wherein plural heat dissipating fins are denselyfixed on one side of the surfaces of an aluminum base plate, and inparticular supply a light weight heat sink with fins having smalldifference of temperature of each part both in the base plate and theheat dissipating fins. Further more, other object of the invention isalso to provide a heat sink with fins having design flexibility, goodworkability and low cost.

One embodiment of the heat sink with fins of the present invention is aheat sink with fins comprising: a group of heat dissipating fins whichcomprise combination of heat dissipating fins made of at least two kindsof metals having different heat conductivity; and a metal base plate onwhich surface portion said group of heat dissipating fins are denselyjointed.

In other embodiment of the heat sink with fins of the invention, eachpiece of said heat dissipating fins forming said group of heatdissipating fins is arranged to locate so as to reduce difference oftemperature both in said metal base plate and in said group of heatdissipating fins.

In other embodiment of the heat sink with fins of the invention, atleast part of said group of heat dissipating fins locating close to aportion of the metal base plate on which a heat generating element isattached are made of copper.

Other embodiment of the heat sink with fins of the invention comprises:a metal base plate to one side of which surfaces a heat generatingelement is attached in close contact; and a group of heat dissipatingfins comprising plural heat dissipating fins of thin metal plates madeof at least two kinds of materials having different heat conductivity,inserted into each of plural grooves formed on other side of thesurfaces of said metal base plate, and then crimped from both directionsof the grooves by pressing to deform portions of the metal base platebetween said grooves, thus fixed on said metal base plate.

In other embodiment of the heat sink with fins of the invention, saidgroup of heat dissipating fins comprise heat dissipating fins made oftwo kinds of metals having different heat conductivity, and part of saidgroup of heat dissipating fins locating close to a portion on which saidheat generating element is attached are made of material having higherheat conductivity than that of heat dissipating fins locating inremaining portion of the metal base plate.

In other embodiment of the heat sink with fins of the invention, saidtwo kinds of metals are copper and aluminum, and said part of said groupof heat dissipating fins locating close to the portion on which saidheat generating element is attached are made of copper and said heatdissipating fins locating in the remaining portion are made of aluminum.

In other embodiment of the heat sink with fins of the invention, saidmetal base plate is made of aluminum.

In other embodiment of the heat sink with fins of the invention, numberof said heat dissipating fins made of copper is within a range from 25%to 75% in total number of said heat dissipating fins.

FIG. 1 shows one embodiment of the heat sink with fins of the presentinvention. As shown in FIG. 1, the heat sink with fins 1 of the presentinvention comprises the base plate 2 made of aluminum, and the group ofheat dissipating fins to be inserted into each of plural grooves formedon one side of the surfaces of the aluminum base plate and mechanicallyjointed on the base plate by being crimped from both sides of thegrooves by pressing to deform the portions of the metal base platebetween the grooves. The group of heat dissipating fins comprise thecopper heat dissipating fins 4 locating in the central portion of thebase plate and the aluminum heat dissipating fins 3 locating on bothsides of the copper heat dissipating fins 4.

FIG. 2 shows another embodiment of the heat sink with fins of thepresent invention. As shown in FIG. 2, as well as FIG. 1, the heat sinkwith fins 1 of the present invention comprises the base plate 2 made ofaluminum, and the group of heat dissipating fins to be inserted intoeach of plural grooves made on the aluminum base plate and mechanicallyjointed on the base plate by being crimped from both sides of thegrooves by pressing to deform the portions of the metal base platebetween the grooves. The group of heat dissipating fins comprise thecopper heat dissipating fins 4 locating in the central portion of thebase plate and the aluminum heat dissipating fins 3 locating on bothsides of the copper heat dissipating fins 4. Embodiments shown in FIG. 1and FIG. 2 are different in the number of copper fins. Morespecifically, the number of copper fins in FIG. 2 is larger than that inFIG. 1.

In the above-mentioned embodiment, the group of heat dissipating finsare mechanically jointed on the base plate. However the group of heatdissipating fins may also be jointed on the base plate by means ofsoldering, silver soldering, welding or the like.

FIG. 3 is a graph showing relationship between copper fin ratio (Morespecifically, ratio of number of the heat dissipating fins made ofcopper in the total number of heat dissipating fins) and thermalresistance. In FIG. 3, the vertical direction shows thermal resistance,and the horizontal direction shows copper fin ratio (%). As clearlyshown in FIG. 3, the thermal resistance is the highest when the copperfin ratio is 0%, and the thermal resistance is the lowest when thecopper fin ratio is 100%. More specifically, within the range of copperratio from 0% to 100%, the higher the copper fin ratio becomes, thelower the thermal resistance becomes.

On the other hand (not shown in the drawing), the higher the copper finratio becomes, the heavier the heat dissipating fins become, and themanufacturing cost thereof increases accordingly. When the copper finratio is below 25%, the thermal resistance is high, thus lowering heatdissipating efficiency of the heat sink. On the other hand, when thecopper fin ratio becomes over 75%, the thermal resistance is notsufficiently reduced anymore. Therefore effectiveness to lower thermalresistance becomes small due to the weight increase and the costincrease.

Therefore, the copper fin ratio is preferable within a range from 25% to75%.

As mentioned above, in the heat sink of the present invention, it isdesirable that the material of the heat dissipating fins locating closeto the portion of the base plate on which the semiconductor chip or thelike is attached has higher heat conductivity than that of the heatdissipating fins locating in the remaining portion of the base plate.More specifically, material of the heat dissipating fins locating closeto the portion of the base plate on which the semiconductor chip or thelike is attached is copper and material of the heat dissipating finslocating in the remaining portion of the base plate is aluminum.

A1050, A6063 and A5055 is applicable for the aluminum material of thebase plate for the heat sink with fins of the present invention, and inparticular pure aluminum (A1050) is desirable.

C1020 and C1100 is applicable for the copper material of heatdissipating fins, and in particular C1020 is desirable. For the aluminummaterial of the heat dissipating fins, the same material as the baseplate is desirable.

A heat sink with fins of another embodiment of the invention comprisesgroups of heat dissipating fins which comprise at least two groups ofheat dissipating fins, which are made of at least two kinds of metalshaving different heat conductivity, the heat dissipating fins of eachgroup being made of same metal, respectively and a metal base plate onwhich surface portion said groups of heat dissipating fins are denselyjointed, wherein a part of the at least two groups of heat dissipatingfins are integrally formed with the metal base plate.

In addition, in the heat sink with fins of the invention, the part ofthe at least two groups of heat dissipating fins are arranged so as tobe at outer sides of said groups of heat dissipating fins. Furthermore,in the heat sink with fins of the invention, the integrally formed partof the at least two groups of heat dissipating fins and the metal baseplate comprises an aluminum extrusion molding product. The integrallyformed part of the at least two groups of heat dissipating fins and themetal base plate may comprise an aluminum diecasting product.

FIG. 5 shows a heat sink having fins in accordance with anotherembodiment of the invention. As shown in FIG. 5, the metal base plate 12and the fins 13 as the part of two groups of heat dissipating fins areintegrally formed, for example, by an aluminum extrusion moldingproduct. In this embodiment, respective outermost two fins 13 areintegrally formed with the metal base plate 12. The thin fins 14 aremade of copper.

Furthermore, the thin fins 14 may comprise two groups of heatdissipating fins, which are made of two kinds of metals having differentheat conductivity, for example, copper and aluminum.

The heat sink with fins 11 of the invention is arranged so that themetal base plate is attached to the semiconductor chip 16 such as a CPUmounted on the printed circuit board 15.

According to the heat sink with fins of the invention as describedabove, since the part of the heat dissipating fins are integrally formedwith the metal base plate, and are arranged so as to be at the outersides of the groups of heat dissipating fin, the relatively thin finslocated between the integrally formed fins may be protected, thusavoiding the problem in which the fins are erroneously deformed when theheat sink with fins are fixed to the electrical device, or the heat sinkwith fins are transported.

In addition, a heat sink with fins comprises a metal base plate to oneside of which surfaces a heat generating element is attached in closecontact, and a group of heat dissipating fins comprising plural heatdissipating fins of thin metal plates made of at least two kinds ofmaterials having different heat conductivity, inserted into each ofplural grooves formed on other side of the surfaces of said metal baseplate, and then crimped from both directions of the grooves by pressingto deform portions of the metal base plate between said grooves, thusfixed on said metal base plate, wherein a part of said at least twogroups of heat dissipating fins are integrally formed with said metalbase plate.

The embodiment of the heat sink with fins described with reference toFIG. 5 may be combined with a part or all of the other embodimentsdescribed with reference to FIGS. 1 to 4.

For example, each piece of said heat dissipating fins forming the groupsof heat dissipating fins is arranged to locate so as to reducedifference of temperature both in the metal base plate and in the groupsof heat dissipating fins. Furthermore, a group of the groups of heatdissipating fins locating close to a portion of the metal plate on whicha heat generating element is attached are made of copper. The metal baseplate is made of aluminum, and the number of the heat dissipating finsmade of copper is within a range from 25% to 75% in total number of theheat dissipating fins.

EXAMPLE

The present invention is explained in more detail by the example.

As shown in FIG. 1, an aluminum base plate with dimension of 80 mmlength, 65 mm width and 5 mm thickness is manufactured. Plural groovesare formed on one side of the aluminum base plate in which the heatdissipating fins are inserted. The copper heat dissipating fins andaluminum heat dissipating fins with the same dimension of 0.6 mmthickness and 30 mm height are inserted into the grooves with 2 mmpitch, and then the heat dissipating fins are mechanically jointed onthe base plate by being crimped from both sides of the grooves bypressing to deform the portions of the metal base plate between thegrooves. The group of heat dissipating fins comprise 30 pieces of heatdissipating fins in which 16 pieces of the copper heat dissipating finslocates in the central portion of the base plate and respective 7 piecesof aluminum heat dissipating fins locate on both sides of the copperheat dissipating fins.

A semiconductor chip of 20 mm×20 mm is attached in close contact to theother side of the heat dissipating fins of the base plate on which noheat dissipating fins are joined, and the condition of the heatdissipation is examined for the heat sink with fins manufactured asdescribed above.

For comparison, as the same as shown in FIG. 1, an aluminum base platewith dimension of 80 mm length, 65 mm width and 5 mm thickness ismanufactured. Plural grooves are formed on one side of the aluminum baseplate to which the heat dissipating fins are inserted. The aluminum heatdissipating fins with dimension of 0.6 mm thickness and 40 mm height areinserted into the plural grooves with 2 mm pitch, and then the heatdissipating fins are mechanically jointed on the base plate by beingcrimped from both sides of the grooves by pressing to deform theportions of the metal base plate between the grooves. The group of heatdissipating fins comprise 30 pieces of aluminum heat dissipating fins.

A semiconductor chip of 20 mm×20 mm is attached in close contact to theother side of the heat dissipating fins of the base plate on which noheat dissipating fins are joined, and the condition of the heatdissipation is examined for the heat sink with fins manufactured asdescribed above.

As the result, the thermal resistance between the temperature of thecooling air and the temperature of the surface of the semiconductor chipis reduced by 0.03 degree Celsius/W on the heat sink with fins of thepresent invention wherein 16 pieces of copper heat dissipating fins arefixed in the center and respective 7 pieces of aluminum heat dissipatingfins are fixed on both sides of the copper heat dissipating fins on thesurface portion of the base plate, compared to the heat sink with finsfor comparison wherein 30 pieces of aluminum heat dissipating fins arefixed on the surface portion of the base plate.

As is clear from the foregoing, according to the present invention, theheat sink with fins having excellent heat dissipating efficiency isobtained together with reducing weight and manufacturing cost thereof.

Although the above example shows the case in which the heat dissipatingfins are arranged so as to be located equally with 2 mm pitch on thebase plate, pitches between the heat dissipating fins can be changed toreduce difference of temperature both in the base plate and the heatdissipating fins.

As described above, according to the present invention the followingheat sink with fins can be provided: More specifically, the heat sinkwith fins in which the group of fins comprising the combination of theheat dissipating fins made of at least two kinds of metals havingdifferent heat conductivity are densely jointed on the surface portionof the base plate, and in particular, the light weight heat sink withfins having small difference of temperature both in the base plate aswell as in the heat dissipating fins.

Additionally, the heat sink having design flexibility, excellentworkability and low cost can be provided by means of the properselection of metals for the base plate and the group of heat dissipatingfins.

What is claimed is:
 1. A heat sink with fins comprising a metal baseplate to one side of which surfaces a heat generating element isattached in close contact, and a group of heat dissipating finscomprising plural heat dissipating fins of thin metal plates made of atleast two kinds of materials having different heat conductivity,inserted into each of plural grooves formed on other side of surfaces ofsaid metal base plate, and then crimped from both directions of thegrooves by pressing to deform portions of the metal base plate betweensaid grooves, thus fixed on said metal base plate, wherein a part ofsaid at least two groups of heat dissipating fins are integrally formedwith said metal base plate.
 2. The heat sink with fins as claimed inclaim 1, wherein said part of said at least two groups of heatdissipating fins are arranged so as to be at outer sides of said groupsof heat dissipating fins.
 3. The heat sink with fins as claimed in claim2, wherein said integrally formed part of said at least two groups ofheat dissipating fins and said metal base plate comprises an aluminumextrusion molding product.
 4. A heat sink with fins comprising groups ofheat dissipating fins which comprise at least two groups of heatdissipating fins, which are made of at least two kinds of metals havingdifferent heat conductivity, said heat dissipating fins of each groupbeing made of same metal, respectively and a metal base plate on whichsurface portion said groups of heat dissipating fins are denselyjointed, wherein a part of said at least two groups of heat dissipatingfins are integrally formed with said metal base plate.
 5. The heat sinkwith fins as claimed in claim 4, wherein said part of said at least twogroups of heat dissipating fins are arranged so as to be at outer sidesof said groups of heat dissipating fins.
 6. The heat sink with fins asclaimed in claim 5, wherein said integrally formed part of said at leasttwo groups of heat dissipating fins and said metal base plate comprisesan aluminum extrusion molding product.
 7. The heat sink with fins asclaimed in any one of claims 4 to 6, wherein each piece of said heatdissipating fins forming said groups of heat dissipating fins isarranged to locate so as to reduce difference of temperature both insaid metal base plate and in said groups of heat dissipating fins. 8.The heat sink with fins as claimed in any one of claims 4 to 6, whereina group of said groups of heat dissipating fins locating close to aportion of the metal plate on which a heat generating element isattached are made of copper.
 9. The heat sink with fins as claimed inany one of claims 4 to 6, wherein said metal base plate is made ofaluminum.
 10. The heat sink with fins as claimed in any one of claims 4to 6, wherein number of said heat dissipating fins made of copper iswithin a range from 25% to 75% in total number of said heat dissipatingfins.